Calculator
Plotly Graph
This chart shows how nominal battery capacity becomes final usable capacity after depth, reserve, efficiency, and health adjustments.
Formula Used
The calculator combines technical battery availability with finance-facing output metrics.
Usable Capacity:
Usable Capacity = Nominal Capacity × DoD × (1 − Reserve Buffer) × Efficiency × State of Health
Annual Usable Energy:
Annual Usable Energy = Usable Capacity × (Planned Cycles ÷ Project Years)
Lifetime Usable Energy:
Lifetime Usable Energy = Usable Capacity × Planned Cycles
Cost per Usable kWh:
Cost per Usable kWh = Purchase Cost ÷ Usable Capacity
Lifecycle Cost per Delivered kWh:
Lifecycle Cost per Delivered kWh = (Purchase Cost + Annual O&M × Years) ÷ Lifetime Usable Energy
NPV:
NPV = −Initial Cost + Σ(Annual Net Benefit ÷ (1 + Discount Rate)^Year)
This helps connect battery performance assumptions to asset valuation, project screening, and cost benchmarking.
How to Use This Calculator
Enter the battery nameplate capacity in kilowatt-hours first. Add the usable discharge percentage, reserve buffer, round-trip efficiency, and current state of health.
Then enter total lifetime cycles, purchase cost, annual operating cost, project duration, discount rate, and the value of each delivered kilowatt-hour.
Press the calculate button. The page will show the result section above the form, along with financial metrics and the capacity waterfall chart.
Use the download buttons to save a result summary as CSV or PDF for reporting, pricing reviews, or investment comparison.
Example Data Table
| Scenario | Nominal Capacity (kWh) | DoD (%) | Reserve (%) | Efficiency (%) | SOH (%) | Usable Capacity (kWh) | Lifetime Energy (kWh) | Cost per Lifetime Delivered kWh ($) |
|---|---|---|---|---|---|---|---|---|
| Residential Backup | 13.50 | 90.00 | 5.00 | 92.00 | 100.00 | 10.62 | 42,476.40 | 0.2142 |
| Small Commercial | 120.00 | 85.00 | 10.00 | 90.00 | 98.00 | 80.97 | 404,838.00 | 0.1709 |
| Fleet Buffer | 250.00 | 80.00 | 12.00 | 88.00 | 95.00 | 147.14 | 662,112.00 | 0.2145 |
| Solar Time Shift | 500.00 | 90.00 | 10.00 | 91.00 | 97.00 | 357.49 | 2,144,961.00 | 0.1329 |
FAQs
1. What is battery usable capacity?
Battery usable capacity is the energy you can realistically access after accounting for discharge limits, reserve protection, efficiency losses, and battery condition. It is usually lower than the nameplate capacity printed by the manufacturer.
2. Why is usable capacity lower than nominal capacity?
Nominal capacity is the rated storage amount. Real projects often keep a reserve buffer, avoid full discharge, lose some energy through conversion, and operate with batteries that degrade over time. Those factors reduce accessible energy.
3. Why include depth of discharge in a finance calculator?
Depth of discharge directly changes the energy you can monetize. Lower discharge limits may improve battery life, but they also reduce delivered energy per cycle. Finance models need both effects to estimate cost and value accurately.
4. What does reserve buffer mean?
Reserve buffer is the portion of capacity intentionally left unused. Operators keep it for battery protection, emergency backup, warranty compliance, or operating flexibility. A higher reserve improves caution, but lowers immediately usable storage.
5. How does state of health affect results?
State of health reflects battery aging relative to original condition. If a battery is at 90% health, it cannot usually deliver its original rated energy. Lower health reduces usable capacity and lifetime economic output.
6. What is cost per lifetime delivered kWh?
It is the total lifecycle cost divided by all expected usable energy delivered across the battery’s planned cycle life. This metric helps compare storage projects with different prices, efficiencies, lifetimes, and operating assumptions.
7. Why does this calculator show NPV?
NPV converts future annual net benefits into present value using the selected discount rate. It helps decide whether the battery project creates enough financial value after considering time, operating cost, and upfront investment.
8. Can I use this for residential and commercial batteries?
Yes. The same logic works for home backup, solar shifting, commercial peak shaving, fleet charging support, and other storage cases. Just enter realistic technical and financial assumptions for the battery system you are evaluating.